Making Waves: Charting Our Future Offshore

Tetra Tech has customized the research vessel Sea Lion V, which includes an office container and equipment to complete offshore geophysical and geotechnical surveys

As a pioneer in coastal engineering and tsunami research, Tetra Tech has worked in the ocean environment since 1966. Today we are moving further offshore to address global demands for energy. Tetra Tech’s engineers and scientists use state-of-the art tools and technologies to provide clean, safe sources of energy in an environmentally responsible manner.

Harnessing the Wind

Wind has powered sailing vessels and grain mills for more than two millennia. Fossil fuels supplanted wind energy at the advent of the industrial revolution, but threats of rising oil costs and concerns about climate change have made wind energy a viable alternative to help power our future.

Tetra Tech is taking its experience building wind towers on land out to sea. “Wind has gained traction in the northeast and mid-Atlantic because of the Atlantic Ocean’s shallow coast,” says Tetra Tech’s Jennifer Daniels, a marine biologist in our Boston, Massachusetts, office and Tetra Tech’s director of offshore energy. “We can install wind turbines 40 miles out to sea along portions of the Atlantic Coast where the ocean floor is less than 200 feet below the surface, suitable for conventional foundation technology.”

With consistent wind speeds and room to spread out, the ocean is a logical alternative to land-based wind turbines, which can measure up to 650 feet tall with blades more than 500 feet long.

Siting wind projects offshore also reduces potential public opposition. “Some people don’t like the aesthetics of large wind turbines,” says Tetra Tech’s Craig MacKay, leader of Tetra Tech’s Electric Generation Initiative. “Placing turbines many miles offshore renders them out of sight and out of mind.”

A promising solution to site towers offshore is floating wind turbines moored with anchors tethered to the ocean bottom. Conventional foundations use jacket or pile supports several hundred feet long. Their installation is limited based on bottom depth and type of underwater terrain. No such restrictions exist with floating turbines.

On the Hywind Demonstration Project, Tetra Tech is testing a deep-water wind turbine off the coast of Maine with Statoil, a Norwegian oil company that deployed the world’s first full-scale, floating wind turbine. Without the geotechnical challenges seen with conventional foundations, floating turbines can be sited at many more offshore locations, thus increasing electric-generating capacity.

“Statoil is using the Hywind project to gain construction experience and operational performance data to develop and demonstrate a more efficient and cost-effective design with a larger turbine and a lighter substructure,” says Daniels. A critical component of this project is the pitch regulator, a special piece of smart technology used in the Hywind turbine that helps stabilize the floating structure.

Tetra Tech also provides services for Dominion Energy’s Virginia Offshore Wind Technology Assessment Project (VOWTAP). VOWTAP is a pilot project consisting of two six-megawatt (MW) turbines with submarine transmission cables that will be in federal waters approximately 26 miles offshore. The project will design and test new foundations for offshore wind turbines in real-world conditions.

“Demonstrating scalability of costs is necessary to establish credibility in the market for commercializing floating wind parks,” Daniels says.

Mapping the Ocean Floor

Just as offshore solutions resolve siting challenges for wind projects in densely populated areas, offshore submarine electric cables have become a popular solution for building new energy infrastructure in coastal urban areas. Land-based overhead transmission lines are difficult to construct, and right-of-way issues pervade the process. Marine mapping helps determine a constructible route for installing oil pipelines and electrical cables.

“Cables can be submerged out in the water and then plugged in onshore for transmission,” MacKay says.

Florida-based wholesale electricity supplier NextEra Energy contracted with Tetra Tech to perform geophysical and geotechnical surveys and marine mapping of the ocean floor off the Massachusetts and New Hampshire coasts. Tetra Tech will provide NextEra comprehensive and reliable data for siting and laying almost 60 miles of submerged electric cable safely and efficiently. The project will be capable of transmitting up to 550 MW of electricity to the greater Boston area.

Tetra Tech’s marine mapping services are highly suitable for offshore energy work. “We can map the sea floor in 2D and 3D, creating photo-like images of the bottom and subbottom,” says Tetra Tech’s Bob Feldpausch, who heads marine mapping in Tetra Tech’s Bothell, Washington, office. “Cables are buried two to three meters under the sea bottom. To achieve that, we seek soft sediments rather than consolidated material or bedrock.” Similarly, pipelines sometimes are laid beneath the sea bottom and sometimes on pads under the pipes.

The marine mapping group now works off the coast of New England, in Puget Sound, and most recently in the Caribbean. Tetra Tech leases the 110-foot Sea Lion V, equipped with sensors and sampling technology, to accommodate the increased demand for mapping services.

The challenges of working at sea include weather, navigation hazards, and most recently, coordination with local New England lobstermen. “We had approximately 60 miles of surveys to conduct in mid-summer—the middle of lobster season,” says Tetra Tech’s Nick Welz, a senior marine scientist in our Boston, Massachusetts, office. The sensor array—a magnetometer, side-scan sonar, and subbottom profiler towed behind the vessel approximately five meters above the sea bed—could have become entangled with commercial lobster pots and gill net buoys.

“We reached out to the lobstermen’s association, posted a flyer in their newsletter, and talked to members in various settings, including holding a public meeting in Gloucester, Massachusetts,” Welz says.

To limit impacts to the lobstermen, Tetra Tech agreed to survey the 60-mile area in 10- to 15-mile segments, each completed in approximately a week. The survey routes were marked clearly by a series of high-flyer buoys that also reflected radar and could be seen at night.

“We subcontracted with Gloucester lobstermen to help get the fishermen’s cooperation” Welz says. “They deployed the buoys, patrolled the routes, and engaged other lobstermen to ensure they were well aware of our survey plans. No lost gear claims were filed, and the survey only caused minor inconveniences.”

Tetra Tech also created a website using geographic information systems technology to enable the Gloucester community to see the ship’s position in real-time during the survey period.

Managing Risks Offshore

While renewable sources of energy account for an increasing share of the market, the bulk of our energy in the near term will continue to come from oil and gas reserves. Working on offshore oil and gas projects poses unique risks to the environment and to worker safety. Oil operators and construction companies must respond quickly to an incident at sea with tools and technologies that minimize the environmental and economic impacts of spills and accidents.

Tetra Tech’s Brazilian operations support the coastal environmental and operational programs of major oil companies such as Chevron, Shell, the BG Group, PETROBRAS, and OGX. We have extensive experience mitigating environmental risks associated with offshore energy exploration and extraction. To assess such risks, our environmental analysts use computational tools that predict the likelihood of spill occurrences, the transport and fate of spilled oil, and the potential environmental effects.

“Such modeling tools can assist in specifying the resources necessary for an emergency response, and during an actual event modeling can help identify those resources at risk and manage the response—setting priorities and determining actions,” says Eduardo Yassuda, director of Tetra Tech’s oceanographic services in Brazil. “Forecasting winds, waves, and currents accurately is crucial to guaranteeing that minimum risk to personnel or damage to equipment occurs in maritime operations.” Accurate forecasts also are necessary to achieve the engineering precision required for completing a project’s specifications.

Tetra Tech engineers typically use two types of models for these analyses. The first calculates the physical properties of ocean currents and winds to determine circulation and transport patterns. The second predicts the geographic location and chemical properties of a pollutant and the relevant biogeochemical characteristics, such as toxicity to marine organisms. This determines the relative risk and associated environmental effects.

The hydrodynamics of sea levels and currents have been difficult to predict in the past, but the focus has shifted. “Since the 1990s, with huge advances in computing resources, we now are more concerned with processes—how to predict a pollutant’s behavior,” Yassuda says. For example, while gasoline evaporates from the ocean surface, the residue remains toxic to sea life. The models calculate the viscosity of some types of crude oil when mixed with seawater, which determines how it behaves in the environment.

Tetra Tech staff use a computer model that reproduces a spill event to calculate possible environmental damage. This information is used to develop mitigation and remediation strategies more effectively, calculate the costs of damage more exactly, and identify responsible parties more reliably.

Tetra Tech routinely runs advanced circulation and transport models to predict the fate and transport of an oil spill in three dimensions to account for the effects of wind and deep-water circulation. To bridge the deep ocean and nearshore estuarine environments, our engineers use the Environmental Fluid Dynamics Code (EFDC) model developed by Tetra Tech’s Dr. John Hamrick. EFDC is a state-of-the-art hydrodynamic model that simulates aquatic systems in one, two, and three dimensions at various spatial and temporal scales to identify ecosystem processes and needs.

In addition to predicting the effects of oil in the ocean, Yassuda and his staff use models in search and rescue missions to locate equipment and develop evacuation procedures. For example, in the Gulf of Mexico, they supported the development of safety procedures for an oil company’s large, floating, offshore oil rig. Our engineers simulated a major storm event and predicted the speed and direction of waves at designated distances. This was essential to calculate when to initiate evacuation procedures and to determine the safest direction in which to evacuate. In Brazil, Tetra Tech used multiple models to help a Brazilian energy company recover a lost wave buoy containing vital data. Starting from its last known position, engineers integrated wind, wave, and current data to predict the geographic area of highest probability in which it could be located—and it was.

Tetra Tech complements its modeling services with monitoring and field sampling to safely manage global offshore operations. Tetra Tech has supported offshore oil and gas exploration and production operations in the Gulf of Thailand for 18 years. Our services include oceanographic and environmental survey work in the oil and gas production area 250 kilometers offshore to characterize site conditions and the effects of exploration and production operations. As part of ongoing research activities, we are collecting 200-centimeter sediment cores to assess the recovery from environmental effects near central processing platforms. The vibracore sampling is conducted using remotely operated vehicles to avoid damaging the seabed production infrastructure near the platforms, according to Tom Grieb of Tetra Tech’s Research & Development Group.

“Several groups of Tetra Tech staff from our Bangkok, Thailand; Lafayette, California; and Bothell, Washington, offices have worked offshore in Thailand,” Grieb says. “The work is demanding but everyone finds it exciting. Offshore assignments are typically three to four weeks, and sampling is conducted around the clock by rotating teams.”

Divers also are in demand for many of our projects. “Tetra Tech is able to support both commercial and scientific diving, which few companies provide,” says Stuart McGahee, senior project manager in our Stuart, Florida, office.

“Our scientific divers are well-suited for the environmental components of offshore energy projects like coral reef restoration and other habitat-related projects,” says Patrick Zuloaga, ecologist and lead diver, who directs a south Florida team of 14 professional divers.

Like the marine mapping group, the commercial diving team is expanding from civil infrastructure work at inland water sites to deep ocean projects. They are experienced providing live images of submerged structures while engineering support personnel above make evaluations. “Any submerged structure is part of our commercial practice,” Zuloaga says.

Charting Our Future

Future energy supplies increasingly will be accessed offshore. As we develop these sources of energy, ports need related infrastructure facilities to safely transmit and distribute the energy generated. Preparing ports may entail the construction of onshore interconnections of submarine cables to the electric transmission system. Dredging may be necessary to lay cables within navigation channels.

“We are in discussions with port authorities on behalf of our private sector clients as we anticipate this work,” says Davie.

Building a viable offshore wind industry in the United States also requires a reliable supply chain to deliver parts and services. Many ports will need to expand, and projects are already under way to accommodate larger ships that will pass through the enlarged Panama Canal.

“Placing these huge wind turbines on barges and moving them to the offshore site may require additional port design work,” Davie says. “These are all opportunities we are tracking closely.”

Tetra Tech is integrally involved in this transformation. Our work with offshore wind turbines, submarine electrical cables, and computer modeling programs that accurately predict sea and atmospheric conditions—supported by marine mapping and environmental sampling services—is expertise our clients need. Equally important, our ability to qualify and quantify potential challenges is helping the offshore energy industry and the public agencies who regulate them learn how best to navigate this frontier.